The benefits of regular aerobic exercise have been well established and accepted. However, due to time constraints, inclement weather, and other reasons, many people are prevented from aerobic activities such as walking, jogging, running, and swimming. In response, a variety of exercise equipment have been developed for aerobic activity. It is generally desirable to exercise a large number of different muscles over a significantly large range of motion so as to provide for balanced physical development, to maximize muscle length and flexibility, and to achieve optimum levels of aerobic exercise. A further advantageous characteristic of exercise equipment, is the ability to provide smooth and natural motion, thus avoiding significant jarring and straining that can damage both muscles and joints.
While various exercise systems are known in the prior art, these systems suffer from a variety of shortcomings that limit their benefits and/or include unnecessary risks and undesirable features. For example, stationary bicycles are a popular exercise system in the prior art, however this machine employs a sitting position which utilizes only a relatively small number of muscles, throughout a fairly limited range of motion. Cross-country skiing devices are also utilized by many people to simulate the gliding motion of cross-country skiing. While this device exercises more muscles than a stationary bicycle, the substantially flat shuffling foot motion provided thereby, limits the range of motion of some of the muscles being exercised. Another type of exercise device simulates stair climbing. These devices also exercise more muscles than do stationary bicycles, however, the rather limited range of up-and-down motion utilized does not exercise the user's leg muscles through a large range of motion. Treadmills are still a further type of exercise device in the prior art, and allow natural walking or jogging motions in a relatively limited area. A drawback of the treadmill, however, is that significant jarring of the hip, knee, ankle and other joints of the body may occur through use of this device.
A further limitation of a majority of exercise systems in the prior art, is that the systems are limited in the types of coordinated elliptical motions that they can produce. Exercise systems create elliptical motion, as referred to herein, when the path traveled by a user's feet while using the exercise system follows an arcuate or ellipse-shaped path of travel. Elliptical motion is much more natural and analogous to running, jogging, walking, etc., than the linear-type, back and forth motions produced by some prior art exercise equipment. Coordinated elliptical motion is produced when the elliptical motions of a user's feet are linked together, so that one foot is forced to move forward in response to the rearward movement of the other foot (in substantially an equal and opposite amount). Limiting the range of elliptical motions utilized by the exercise systems can result in detrimental effects on a user's muscle flexibility and coordination due to the continued reliance on the small range motion produced by some prior art exercise equipment, as opposed to the wide range of natural elliptical motions that are experienced in activities such as running, walking, etc. Further, the exercise systems in the prior art produce various types of forced coordinated elliptical motion. There is a continuing need for an exercise device that provides for smooth natural action, exercises a relatively large number of muscles through a large range of motion, and allows for flexibly coordinated elliptical motion, i.e., elliptical motion that is substantially coordinated but still allows for some independent or uncoordinated motion between the movement of the user's feet.